Book People Archive

Re: response to Andrew (& a couple of tips)

Okay, I wrote this as a response to some email that I thought was a post
to the mailing list.  JMO pointed out that it was in fact an email when I
posted it (thanks, John), so here it is again with the parts of the email
summarised [in square brackets] rather than quoted:

First some acronyms:

CFF (Critical Fusion Frequency) means the lowest rate of flicker that you
can't see.

a CRT (Cathode Ray Tube) is the display in a normal TV or monitor screen,
as opposed to newer, flatter and more expensive (per unit area) displays
such as you might find in 'ebook readers'.

[complaint that CFF varies from person to person]

CFF does varies from person to person, of course, and mentioning an 'exact
number' was misleading of me.  I do think I'm right in saying that the
values of 100Hz for CFF would be very high -- you can get CRTs with that
vertical refresh rate, or higher, I think.  I've never heard of people
having a CFF higher than 90Hz, but maybe they do.

Mind you, I admit I was being a bit literal minded in interpreting "I can
see all monitors flicker".

On the other hand, even when you can't *see* the flicker, research has
claimed to show effects on vision, and as far as 'e-book readers' go, this
is the real problem, I think.  It seems that you need to go above the CFF
(I don't think it's known by how much) to make reading a book on a screen
feel like reading it on paper.

This paper about the effects of flicker at or just above the CFF looks
interesting, but I haven't read it, I suspect it's in German, and I can't
find it in the standard database to check:

Ziefle, M; Zeitschrift fur arbeits-und organisationspsychologie, vol 45,
p. 15 (2001)

and on display (spatial) resolution, in English:

Ziefle, M; Human Factors, vol. 40, p 554 (1998)

[suggestion that interference patterns may cause visible flicker]

Hmm.  I hadn't thought of that.  :)

[suggestion to use TFT LCD displays, since they don't have any flicker]

I'm told even TFT LCD displays do flicker in practice, because they are
modulated to increase the number of levels of intensity (and hence 'no. of
colours') they can display.  I don't recall why they're limited in this
way; it seems likely some of the new displays won't suffer from this.  It
could be argued that text-only books don't have much need for this, but in
practice resolution is also important, and you can improve that (in
effect) by increasing the number of intensities available.  There is a
trade-off.

In the longer term (brace yourselves, paper book-lovers) it may be that
the best displays will be better than any flat image can be, even in
principle, because they will work by directly painting the images onto
your retina with laser beams, thus correcting for any optical deficiencies
in your eyes.  This has been done, and there is a company developing it,
but it doesn't work well yet and will likely be expensive for a long
while.


John